Speaking of foam, I did find some pretty nice sheets. I didn't pick up the memory foam ones (would have been PERFECT to make earpads, they were super soft) but only the regular ones... still one of the softer foams I found. It's just not very thick so I'd have to stack donuts the day I start making pads again.
Though honestly foam's own breathability probably isn't so much of an issue... the more plush and flush the pads sit on your face the warmer it gets. Even with velours... some velour pads have leather/pleather backings too, yet still feel decently cool simply due to the foam not being entirely form-fitting like softer memory foam.
Well, I'm far from being any expert at velour pads (mostly only tried Beyer and AKG ones) so any input to outrule what I just wrote would be helpful for my own learning as well.